Optical light curves and spectra of the Type la supernova 1986G in NGC 5128 (Centaurus A) are presented. SN 1986G was discovered approximately one week before maximum light. The initial rate of decline of the B light curve was remarkably fast and characteristic of the infrequently observed Pskovskii photometric class ß = 12. Although the spectral evolution closely resembled that of the more common "slower" photometric classes of Type la supernovae, subtle differences in the maximum-light spectra were detected. The expansion velocity of the photosphere of SN 1986G decreased rapidly at early phases, suggesting that the outer-envelope density gradient was less steep than in supernovae with smaller values of ß. SN 1986G appears to have been heavily obscured (E(B -V) = 0.90 ± 0.10) by the dust lane of NGC 5128. This circumstance accounts for the strong interstellar-absorption lines of Ca n H and K and Na ID observed in the spectra as well as for several weaker absorption features that we identify with the diffuse interstellar bands.SN 1986G provides graphic confirmation of the existence of intrinsic differences in the optical light curves and spectroscopic properties of Type la supernovae. Consequently, these objects must be used with considerable caution as cosmological standard candles. On the basis of the very close resemblance of SN 1986G to SN 19711 in NGC 5055, we derive a relative distance of D NGC5128 / D NG c5055 = 0.39 ± 0.04. Further distance estimates are hampered due to the lack of other well-observed Type la supernovae with ß = 12.
Spectra of giant stars in the intermediate-age galactic cluster NGC 752 and in the old cluster M 67 have been examined for the presence of Li I Á.6707. The lithium feature is not present in any of the M67 giants observed, leading to upper-limit abundances of loge(Li) < -1.0 to 0.3. While lithium is not present in most NGC 752 giants, the feature is strong in two giants, Heinemann 77 and 208, log e(Li) = +1.1 and +1.4, respectively. In the remaining giants in NGC 752, log e(Li) < 0.5. The absence of lithium in M67 giants may be because these giants evolve from progenitors in the region of the main-sequence lithium dip.
Cytomixis is reported to be a uniform phenomenon in the context of fertilization during spermatogenesis of animals and in some lower groups of plants where oogamous reproduction prevails. However, the phenomenon is versatile in flowering taxa as it lacks uniformity in occurrences, causes, formation of intercellular bridges, involvement of number of cells in a cluster, evolutionary significance among others. A review on cytomixis is conducted with an objective that it may offer a scope to unravel some of the ambiguities associated with it and provide further information on cell, reproductive, structural and evolutionary biology.
Achromatic wave plates are ideal components for use with tunable and multiline laser systems, broadband sources, and in astronomical instrumentation. The present study deals with the design and characteristics of two different quarter-wave achromatic retarders in the 500-700 nm range, using a cascaded system of two birefringent plates. The first of these shows a variation of less than ±0.5°, whereas the second system shows a variation of ±4° where the azimuth remains constant. Finally, a comparison between the two systems is made. The succinct and simple Jones matrix formalism has been used to derive the general expression for the equivalent retardation and azimuth of the combinations. It appears that the proposed arrangement has the promise of producing good achromatic combinations.
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